1. Field of the Invention
This invention relates to a tubular shaft construction and especially to a hollow shaft having alternate areas of surface convexity and concavity to provide integral reinforcement for increased rigidity.
The shaft construction of this invention is particularly adaptable for sports playing equipment having elongated or slender medial sections or handles such as for golf clubs, ski poles, squash rackets, and the like.
2. Description of the Prior Art
Sports apparatus as currently being manufactured is subjected to shock or impact stresses, and as a result must be designed to accommodate these varying load conditions. It is important in such sport activities as golf, skiing, tennis, etc., that the respective equipment, i.e. golf club, ski pole, tennis racket, be as light as practicable so that it can be easily handled, yet should be structurally capable of withstanding high impact blows.
Devices of the prior art, such as golf clubs were accordingly improved by substituting some of the previously used materials, e.g. wooden shafts, with tubular metal shafts having higher yield stresses and also by providing cross-sectional shapes that afforded maximum rigidity.
Other shaft constructions such as disclosed in U.S. Pat. Nos. 1,983,074 and 2,001,643 utilized longitudinal undulations or grooves formed in a cylindrical tubular shaft. In many of these shafts the grooves constituted ribs or corrugations extending from one end of the shaft to the other end. While these reinforcement systems offered added strength, they did so at the expense of additional weight, bulkiness, and cost. Furthermore, this previously disclosed construction is primarily concerned with strengthening the shaft along its vertical axis with minimum resistance strength being provided for torsional stresses.
In addition, attempts have also been made at stamping, corrugating or embossing a design which is pressed into the surface of the shaft, ostensibly for providing added rigidity, but in many cases merely improving only the esthetic appearance.
This invention overcomes many of the shortcomings of the prior art by providing a three-dimensional redistribution of the tubular material for increased structural rigidity without added weight.